An unlicensed frequency band is used for wireless communication of certain wireless communication networks, such as WiFi™ wireless local area networks that operate in the 2.4 GHz band in the United States. Interference mitigation in a wireless network that operates in an unlicensed frequency is important due to the limited bandwidth and coexistence issues.
WiFi devices employ the carrier sense multiple access (CSMA) protocol in order to detect energy on their channel and only transmit when the channel is not being used. In particular, if the energy detected is above a CCA threshold level, then the channel is deemed to be in-use and the transmission attempt is deferred. For example, in the IEEE 802.11n wireless local area network (WLAN) protocol, the CCA threshold for 20 MHz transmissions is −62 dBm.
Because a WiFi network operates in an unlicensed frequency band, there may be many wireless devices on a given channel that do not follow a “listen-before-talk” protocol. As a result, when these non-WiFi interferers are present, they make no effort to share the channel with WiFi devices. For instance, it is well known that a wireless camera can produce a transmission having a wide bandwidth at an unrestrained power level. As a result, the WiFi devices will always defer to the non-WiFi interferer's transmissions, which leads to a significant degradation of network throughput, perhaps even reducing throughput to zero in the presence of certain interferers.